In the case of France, there are some low hanging fruits. The two main airports in Paris, which are also the country's main hubs, are connected to the train net

In the case of France, there are some low hanging fruits. The two main airports in Paris, which are also the country's main hubs, are connected to the train network. But to transfer from most of Paris's train stations to the airport train, you have to navigate a maze of tunnels and staircases, and bus and metro lines. I would seriously have to think about how to transfer from Montparnasse to CDG, and I've lived there. Having better, clearer connections between the main train stations in Paris would benefit all train travelers, not just those going to the airports. There is a planned dedicated express train from Gare de l'Est to one of the airports: https://en.wikipedia.org/wiki/CDG_Express https://en.wikipedia.org/wiki/CDG_Express